Blind spot

The team, from the London School of Hygiene and Tropical Medicine and the UCL Institute of Child Health, gave questionnaires to nearly 3,000 families asking if their child was obese, overweight, underweight or a healthy weight.

The results showed that nearly a third, 31%, of parents underestimated the weight of their child.

An accurate diagnosis kicked in only at the very high end of the scales.

“We need to find some tool to educate parents, when their child is born, what they should expect a child’s size to be and not to be afraid of talking to parents over fears they, or the child, will react badly,” Prof Viner said.

‘Role models’

Commenting on the findings, the chief executive of the Royal Society for Public Health, Shirley Cramer, said: “School education from a young age should focus on the importance of active lifestyles and healthy diets to ensure our society is one that understands the relationship between diet and good health.

“Parents are key role models for their children and it is imperative they are aware of all the factors that can influence health.

“However, it is not just the role of the parents, society as a whole needs to help enforce messages about eating well.”

She said restricting junk food advertising would help as would better calorie labeling on food.

Tam Fry, from the Child Growth Foundation, told the BBC: “To the obesity specialist it is incomprehensible that parents cannot tell if their children are overweight.

“You sometimes have to wonder if they are in total denial, but when you realise that even health professionals may often have difficulty in recognising obesity in their patients, the enormity of our obesity epidemic sinks in.

“The knock-on risk of extreme overweight to the individual’s and country’s health cannot be emphasised enough.”